A wide variety of emergency breathing equipment has previously been developed, such as the protective hood with CO.sub.2 absorbant described in Werjefelt, U.S. Pat. No. 4,627,431, and the multilayered hood with elastomeric neck seal described in copending, coassigned U.S. application Ser. No. 120,533, filed Nov. 13, 1987. This type of equipment generally includes a protective hood, a source of oxygen and a means to remove, from the hood interior, the carbon dioxide exhaled by the wearer.
Lithium hydroxide (LiOH) is one compound commonly used to absorb the carbon dioxide. LiOH is often preferred as an absorbent because it provides acceptable absorption characteristics with acceptable weight. Particularly in aircraft applications, weight is an important consideration.
Lithium hydroxide is readily available in powder form, which provides a surface area that maximizes its effectiveness as an absorbant. However, the powder dust is a respiratory irritant, and should therefore be isolated from the wearer.
Previously, scrubbers were constructed by impregnating felt with LiOH powder by putting the two together in a ball mill. The resulting loaded felt was encased in an envelope of semipermeable membrane that allowed gas flow through the envelope while retaining the LiOH. Heat sealing of such envelopes was also used to maintain the uniform distribution of the LiOH powder within the envelopes.
While such previous techniques and designs were satisfactory, continuing effort has been devoted to a CO.sub.2 absorbant system that would provide improved balance among maximum absorption, isolation from the wearer, ease of manufacture and low cost and weight.